In U.S. Pat. Nos. 3,813,320 and 3,834,988 (of which the applicant herein is a co-inventor), there are shown various media and various microorganisms which produce glucose isomerase. U.S. Pat. No. 3,813,320 involves the use of Aerobacter levanicum in a two-stage fermentation procedure using unpurified hardwood sulfite liquor as part of the medium in the second stage where the glucose isomerizing enzyme is produced. U.S. Pat. No. 3,834,988 shows the production of glucose isomerizing enzymes from an organism of the Actinoplanes genus in a medium whose principal constituent is corn steep liquor which has had the sludge removed. In the patent and scientific literature there are disclosures of other microorganisms which produce glucose isomerizing enzymes. Some of these enzymes convert D-glucose to D-fructose through one or more chemical intermediates (e.g., D-glucose-6-phosphate) but these enzymes do not appear to be practical for industrial use at the present time.
More promising are enzymes known as glucose isomerase that convert D-glucose to D-fructose directly. A number of these enzymes have been prepared from microorganisms of the genera lactobacillus, Pseudomonas, Pasteurella, Leuconostoc, Streptomyces and Aerobacter (see review by Yamanaka in Biochem. Biophys, Acta 151, 670-680). In order that a significant quantity of glucose isomerase be formed by any of the foregoing microorganisms, xylose or xylan must be present in the growth medium to induce the enzyme. Pure xylose is relatively expensive, and when xylan is used in the growth medium, the microorganism must also produce enzymes capable of hydrolyzing the xylan.
In order to overcome the expense of growing the microorganism in a xylose or xylan-containing medium, efforts have been expended to obtain a bacterium that will produce the enzyme constitutively. Lee, Hayes and Long (U.S. Pat. No. 3,645,848) have disclosed that certain strains of microorganisms belonging to the genus Arthrobacter are capable of producing enzymes that directly convert glucose or xylose to the corresponding ketose when grown in a medium from which xylose or xylan is absent. Relatively small amounts of isomerase are produced and the growth medium requires relatively expensive nitrogen sources, such as yeast extract and meat protein.